There are a number of environments wherein a virtually closed vessel contains a fluid that is subjected to a wide range of temperature fluctuations. Such conditions can cause the fluid to expand or contract in response to those temperature variations, and simultaneously absorb or discharge gases. In order to accommodate these changes, such vessels are commonly provided with "breathing" vents which do accommodate pressure changes, but the historically known constructions for such breathing vents often permit the admission of contaminants from outside the vessel.
A transmission housing epitomizes a virtually closed vessel, and because of the intricate mechanism contained within a transmission housing, the presence of contaminants can be detrimental to the operation and maintenance of the transmission. As is well known in the art, transmission housings have heretofore been provided with rather intricate venting arrangements by which to equalize the pressures within the housing relative to the ambient pressure outside the housing, and at the same time attempt to preclude the admission of contaminants. Such prior known venting arrangements have required additional, intricate machining operations in order to prepare the housing for receiving the venting mechanism, and the venting mechanism has usually been separate from the access aperture or fill tube, and/or the cap by which the access aperture is selectively opened and closed. Historically, therefore, venting arrangements had to have been separately manufactured and installed.
The prior art is also replete with ullage rod arrangements which are separate from both the venting arrangement and the sealing cap for the fill tube. As a result, the production costs to make, install and maintain the aforesaid prior art arrangements unduly increased the costs of the transmission housing.